1. Field of the Invention
The present invention relates to a light-emitting device as well as to a lens used in the light-emitting device.
2. Description of the Related Art
In order to cause a side surface of a rod-shaped element formed from a transparent resin, and the like, to illuminate, a light-emitting device configured so as to introduce light from an LED lamp serving as an LED light source to an end face of the rod-shaped light-emitting element has already been put forward (Patent Document 1 and Patent Document 2).
Since the end face of the rod-shaped light-emitting element has a small area, light from an LED chip must be converged to the end face in order to sufficiently introduce light into the rod-shaped light-emitting element. For this reason, in Patent Document 1, an LED lamp is placed in a case-shaped joined element, and light from the LED lamp is converged to an end face of the rod-shaped light-emitting element by utilization of a reflection surface of the interior surface of the joined element.
Patent Document 1: JP-A-2005-29030
Patent Document 2: JP-A-2006-13087
An invention described in Patent Document 1 is on the premise that a plurality of LED lamps are arranged with respect to an end face of a rod-shaped light-emitting element (see FIG. 4 of Patent Document 1, and the like). The reason for this is that a sufficient quantity of light is ensured and that the light is supplied to a peripheral surface of the rod-shaped light-emitting element, thereby reliably illuminating the peripheral surface.
From the viewpoint of a reduction in the number of components, realizing an LED lamp as a single component has been requested. The present inventors have conducted a study to meet such a request and found the following problem.
Specifically, in a single LED lamp, the centerline of the LED lamp is aligned to the centerline of the rod-shaped light-emitting element in order to uniformly supply light to the end face of the rod-shaped light-emitting element. In order to converge light from the LED lamp and reliably irradiate the end face of the rod-shaped light-emitting element with the light, a lens must be interposed between the LED lamp and the rod-shaped light-emitting element.
When a common condensing lens is used, light from the LED lamp can be reliably converged to an end face of the rod-shaped light-emitting element. However, light in proximity to the centerline of the LED lamp becomes substantially parallel to the centerline. Accordingly, light still remains substantially parallel to the centerline even in a rod-shaped light-emitting element and hardly goes out of a side surface (a light-emitting face) of the rod-shaped light-emitting element.